Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555
May 25, 1988
Information Notice No. 88-30: TARGET ROCK TWO-STAGE SRV SETPOINT
DRIFT UPDATE
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert recipients to continuing
problems associated with setpoint drift occurring in Target Rock two-stage
safety/relief valves (SRVs) originally described in Information Notices (INs)
82-41, 83-39, 83-82, and 86-12 (References 1 - 4). It is expected that re-
cipients will review the information for applicability to their facilities
and consider actions, if appropriate, to avoid similar problems. However,
suggestions contained in this information notice do not constitute NRC require-
ments; therefore, no specific action or written response is required.
Background:
On July 2, 1982, at Hatch Unit 1, all 11 Target Rock two-stage SRVs failed to
open at their setpoints of 1080 psig, 1090 psig, and 1100 psig. Pressure in
the reactor coolant system (RCS) rose to 1180 psig before three SRVs on one
steamline opened and relieved RCS pressure rapidly. This incident focused
concern on a problem that was beginning to be seen in those SRVs, called
"setpoint drift".
The Georgia Power Company, the General Electric Company (GE), and the Target
Rock Company initiated a study of the cause of the event at Hatch Unit 1.
Other utilities that had installed two-stage Target Rock SRVs joined Georgia
Power in an owners' group to look into the nature of the problem and its
solutions.
Similar problems had been observed throughout the industry and reports in-
dicat-ed that the number of valves affected and the extent of the observed
setpoint drift had been increasing. The problem was ultimately identified
as one or both of two situations: (1) binding in the labyrinth seal area
caused by tolerance buildup during manufacturing or (2) disc-to-seat bonding
caused by oxides of the disc and seat material forming a continuous film and
inhibiting disc movement.
8805200030
. IN 88-30
May 25, 1988
Page 2 of 3
To address these problems, additional maintenance was performed to refurbish
valves and replace parts found to be out of tolerance in the labyrinth seal
area. This proved to be effective in some cases; however, problems caused by
disc-to-seat bonding continued. A material, PH13-8Mo, whose oxide would not
form a continuous film with the oxide of the seat material, was chosen for new
discs. A trial test of valve performance after about 50% of the valves on a
plant had new discs installed is currently being conducted.
Test Results:
Initial results of the test of the new discs were obtained in May of 1987 when
the Hatch Unit 1 valves were tested. Of the five valves that had new discs
installed, four had pilot valves that leaked before the test. Only one of
these four pilot valves did not leak after the test. The valve that did not
leak before the steam test had first been tested with nitrogen gas (N 2) to
determine if the disc was stuck. It lifted at 5 psig N 2. The remaining four
valves lifted within 2% of setpoint. The technical specification (TS) limit
is ñ 1% of the setpoint. One of these leaked so much that the bonnet pressure
could not be stabilized and the delay time (time between lift of the pilot
disc and the lift of the main disc) was excessive. Subsequently, the
remaining valves were tested. Test values for all 11 valves are given in
Table 1.
Disc numbers 313 and 1186, which are new discs, showed a lighter-color oxide
which was less-adherent and softer in the steam area than was seen on the old
discs in previous tests. Also, the seating area was bright and was not banded
with the apparent cleft of the corrosion seen on the old discs in previous
tests. Discs 1189 and 1002 showed similar corrosion properties, but were
obviously steam drawn around the entire circumference. Disc 1189 showed signs
that foreign material had been lodged between the disc and the seat. A stabi-
lizer disc (Stellite) from one valve exhibited the same darker, harder,
more-adherent corrosion as had been seen previously on the old (Stellite)
discs. The decision was made to turn the new disc over to GE for testing and
to replace the new discs with other new discs, but not to replace the old
discs at that time.
Brunswick Unit 2 completed its testing for this cycle in early 1988. Initial
reports indicate that valves with the PH13-8Mo discs lifted at +1.9%, -0.1%*,
-1.2%, +0.6%, and +4.0% of their setpoint. One valve was not tested. The
old-style valves, with the Stellite 6 discs, lifted at +9.3%, -1.4%, -0.2%,
+0.6%, and +2.6%*. Details are shown in Table 2.
Hatch Unit 2 test results were also recently received. They show the valves
with PH13-8Mo discs lifted at +2.9%, +1.8%, +0.7%, and -1.1%. The valves with
the Stellite discs lifted at +1.5%, +0.3%, +4.1%, +0.2%, +2.8%, and +1.6%.
Details are shown in Table 3.
Based on available test results, the valves with new discs appear to perform
better than valves with old discs, and valves with old discs appear to perform
better than they did in the past.
(*Second lift - the recorder was not running when the disc was first lifted).
. IN 88-30
May 25, 1988
Page 3 of 3
If, when the analysis of the data is completed, the cause of the +4.0% drift
on the Brunswick Unit 2 valve and the +2.9% drift on the Hatch Unit 2 valve
can be determined, then PH13-8Mo may be proven to be an acceptable substitute
for Stellite 6. The NRC will continue to follow the testing program.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Mary S. Wegner, AEOD
(301) 492-7818
Attachments:
1. Table 1, 1987 Test Results for Hatch Unit 1 Target Rock SRVs
2. Table 2, 1988 Test Results for Brunswick Unit 2 Target Rock SRVs
3. Table 3, Test Results for Hatch Unit 2 Target Rock SRVs
4. List of Recently Issued NRC Information Notices
References:
1. Information Notice No. 82-41, "Failure of Safety/Relief Valves to Open at
a BWR."
2. Information Notice No. 83-39, "Failure of Safety/Relief Valves to Open at
BWR - Interim Report."
3. Information Notice No. 83-82, "Failure of Safety/Relief Valves to Open at
BWR - Final Report."
4. Information Notice No. 86-12, "Target Rock Two-Stage SRV Setpoint Drift."
. Attachment 1
IN 88-30
May 25, 1988
Page 1 of 1
TABLE 1
1987 TEST RESULTS FOR HATCH UNIT 1 TARGET ROCK SRVs
Valve Identifier Setpoint Leak[1]
Disc SN TS As-Found Var Prior Post
New 1189 1090 1072 -1.65% Yes Yes
New 313 1080 1096 +1.48% Yes No
New 1002 1080 1101 +1.94% Yes Yes
New 1186 1100 5 (N2) LT 1% No No
New 1190[2] 1100 1083 +1.55% Yes Yes
Old 1006 1090 1093 LT 1% Yes Yes
Old 1187 1090 1076 -1.28% Yes Yes
Old 1011 1080 1146[3] +6.11% No No
Old 1009 1080 1053 -2.50% Yes Yes
Old 1004 1090 1101 +1.01% Yes Yes
Old 1003 1100 1116 +1.45% Yes Yes
SN = Serial Number
TS = Technical Specifications
Notes:
[1] Pilot disc leakage.
[2] Originally mounted on a Hatch body, but was removed due to leakage past
the main disc. Remounted on a slave (Wyle) body. Pilot leakage was so
great that the 30-minute stabilization of the bonnet temperature was
waived.
[3] Failed to lift when tested on 5 psig nitrogen.
. Attachment 2
IN 88-30
May 25, 1988
Page 1 of 1
TABLE 2
1988 TEST RESULTS FOR BRUNSWICK UNIT 2 TARGET ROCK SRVs
Valve Identifier Setpoint
Part Number Disc SN SL TS As-Found Var Leak[1] N2 Test
2B21-F013A New 1109 A 1105 1126 +1.9% Yes No
2B21-F013B Old 1103 A 1125 1230 +9.3% Yes No
2B21-F013C Old 1099 B 1105 1090 -1.4% No Failed
2B21-F013D New 1102 B 1115 1114[2] -0.1%
2B21-F013E Old 1105 B 1115 1113 -0.2% Yes No
2B21-F013F Old 1091 C 1105 1112 +0.6% No Failed
2B21-F013G New 1106 C 1105 1092 -1.2% Yes No
2B21-F013H New 1107 D 1115 1122 +0.6% Yes No
2B21-F013J New 1108 D 1125 1170 +4.0% Yes No
2B21-F013K Old 1101 C 1115 1144[2] +2.6%
2B21-F013L New 1104 B[3]
SN = Serial Number
SL = Steamline
TS = Technical Specifications
Notes:
[1] Pilot disc leakage.
[2] Second lift, valve was inadvertently lifted without recorder running.
[3] Retainer bolts removed, spring preload lost, no as-found test done.
. Attachment 3
IN 88-30
May 25, 1988
Page 1 of 1
TABLE 3
TEST RESULTS FOR HATCH UNIT 2 TARGET ROCK SRVs
Valve Identifier Setpoint
Disc SN TS As-Found Var Leak[1]
Old 301 1100 1116 +1.5% Yes
New 302 1100 1132 +2.9% Yes
Old 303 1110 1114 +0.4% Yes
New 306 1110 1130 +1.8% Yes, badly
New 307 1110 1118 +0.7% Yes, badly
New 308 1090 1078 -1.1% Yes
Old 310 1090 1135 +4.1% No
Old 312 1090 1092 +0.2% Yes
Old 314 1090 1121 +2.8% Yes
New 315 1100 1109 +0.8% Yes
Old 1001 1100 1118 +1.6% Yes
SN = Serial Number
TS = Technical Specifications
Notes:
[1] Pilot disc leakage.
. Attachment 4
IN 88-30
May 25, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-29 Deficiencies in Primary 5/24/88 All holders of OLs
Containment Low-Voltage or CPs for nuclear
Electrical Penetration power reactors.
Assemblies
88-28 Potential for Loss of 5/19/88 All holders of OLs
Post-LOCA Recirculation or CPs for nuclear
Capability Due to power reactors.
Insulation Debris Blockage
88-27 Deficient Electrical 5/18/88 All holders of OLs
Terminations Identified or CPs for nuclear
in Safety-Related power reactors.
Components
85-35, Failure of Air Check 5/17/88 All holders of OLs
Supplement 1 Valves to Seat or CPs for nuclear
power reactors.
88-26 Falsified Pre-Employment 5/16/88 All holders of OLs
Screening Records or CPs for nuclear
power reactors and
all major fuel
facility
licensees.
88-25 Minimum Edge Distance for 5/16/88 All holders of OLs
Expansion Anchor Bolts or CPs for nuclear
power reactors.
88-24 Failures of Air-Operated 5/13/88 All holders of OLs
Valves Affecting Safety- or CPs for nuclear
Related Systems power reactors.
88-23 Minimum Edge Distance for 5/16/88 All holders of OLs
Expansion Anchor Bolts or CPs for PWRs.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
